Folding and crystallization conditions of menbrane protein supercomplexes

本课题对膜蛋白的折叠机制和结晶方法进行了研究，得出了以下结论。细胞内跨越生物膜的膜蛋白超复合体的三维结构是通过暴露在含水介质中的亲水环以及置于膜疏水环境下的α螺旋来稳定的，这些螺旋之间提供氢键和静电相互作用。因此，用覆盖疏水表面的洗涤剂增溶似乎是分离这种类型的蛋白质复合体而不变性的最好方法。蛋白质微囊之间稳定晶态的特异性相互作用很可能是亲水表面之间的相互作用，这表明同源膜蛋白大的比小的更有利于结晶。在许多同源蛋白中，只有从牛心线粒体中分离出的最大的细胞色素C氧化酶和细胞色素Bc1复合体被结晶，这一事实支持了这一结论。附着在膜蛋白疏水表面的洗涤剂分子的结构可以控制蛋白分子亲水性表面之间的特定相互作用，从而决定结晶条件。控制机制并不像Michel等人提出的那么简单。

This research project has provided the following conclusion about the folding mechanism and the crystallization method of membrane protein. Three dimensional structure of the membrane protein supercomplexe spanned across the biological membrane in the cell is stabilized by hydrophilic loops exposed to aquaous medium as well as by alpha-helices placed under the ydrophobic environment in the membrane which provide hydrogen bonds and electrostatic interactions between these helices. Thus, solubilization with a detergent which covers the hydrophobic surface seems the best method for isolation of this type of protein complex without denaturation. The specific interaction between the protein melocules which stabilizes the crystalline state is likely to be the one between the hydrophilic surfaces, suggesting that larger homologous membrane protein is better for crystallization than the smaller one. This conclusion is suppoted by the fact that only the biggest cytochrome c oxidase and cytochrome bc1 complex, isolated from beef heart mitochondria, among many homologous proteins have been crystallized. Structure of the detergent molecules which attach to the hydrophobic surfaces of membrane proteins could control the specific interactions between the hydrophilic surface of the protein moleules to determine the crystallization conditions. The control mechanism is not so simple as has been proposed by Michel et al.